As concerns surrounding traditional energy sources persist, investigation into alternative forms of energy are becoming increasingly important. In particular, environmental and political concerns associated with emissions of combustion based energy systems can not be ignored. In an effort to reduce dependence on these types of energy supplies and methods, therefore, the focus is likely to be on devices capable of generating electricity by consuming plentiful or renewable supplies of fuels with low or zero emissions.
Alternatives to internal combustion engine powered vehicles have included various types of battery powered electric vehicles. Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized; the cathode contains or consumes an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When a battery is used as an electrical energy source in a device, such as a vehicle, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
A problem associated with most known battery powered vehicles, however, is the constant need for recharging, due to the limited amount of energy a battery can hold in a single charge. In the current state of the art, recharging a battery requires taking the vehicle out of service. Current methods of recharging require the vehicle to be brought to a standstill, and are time-consuming and tedious, particularly since they must be performed frequently.
Fuel cells, therefore, have been explored as a means for powering electric vehicles and reducing the constant need to recharge the vehicle from off-board sources. Fuel cells electrochemically convert hydrocarbons or hydrogen to electricity with low or zero emissions. Because they are compact in structure, high in efficiency, and low in pollutants, fuel cells provide several advantages for use in vehicle transportation. Accordingly, fuel cells appear to be well suited for adaption to vehicle applications.
A drawback associated with known fuel cell systems, however, is that they are not economically viable for applications in which the power rating of the fuel cell must meet propulsion demands. In motor vehicle applications, for example, a fuel cell system designed to provide sufficient power required by the vehicle for cruising, let alone for peak surge, would be prohibitively expensive. While various known systems have attempted to exploit the advantages of designating a surge battery to meet peak demand in motor vehicle applications, none has satisfactorily overcome the size-constraints for on-board integration.